Clues from the prompt emission of grb 080319b

Yuan Chuan Zou*, Tsvi Piran, Re'em Sari

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

25 Scopus citations


The extremely bright optical flash that accompanied GRB 080319B suggested, at first glance, that the prompt γ -rays in this burst were produced by synchrotron self-Compton (SSC). We analyze here the observed optical and γ spectra. We find that the very strong optical emission imposes, due to self-absorption, very strong constraints on the emission processes and puts the origin of the optical emission at a very large radius, almost inconsistent with internal shock. Alternatively, it requires a very large random Lorentz factor for the electrons. We find that SSC could not have produced the prompt γ -rays. We also show that the optical emission and the γ -rays could not have been produced by synchrotron emission from two populations of electrons within the same emitting region. Thus, we must conclude that the optical emission and the γ -rays were produced in different physical regions. A possible interpretation of the observations is that the γ -rays arose from internal shocks but the optical flash resulted from external shock emission. This would have been consistent with the few seconds delay observed between the optical and γ-ray signals.

Original languageAmerican English
Pages (from-to)L92-L95
JournalAstrophysical Journal
Issue number2 PART 2
StatePublished - 2009

Bibliographical note

Funding Information:
We thank P. Kumar, R. Mochkovitch, and Y. Fan for discussion. This work is supported by the Israel Science Foundation Center of Excellence in High Energy Astrophysics and by the Schwartzmann University Chair (T.P.), by a Marie Curie IRG and NASA ATP grant (R.S.), by the National Natural Science Foundation of China grant 10703002 and a Lady Davis Trust Post-Doctoral Fellowship (Y.C.Z.).


  • Gamma rays: bursts
  • Radiation mechanism: nonthermal


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